Twist-drill.



I No. 867,639. PATENTED OCT. 8, 1907.

1G. J. BRAGG.

' TWIST DRILL.

APPLIOATION FILED MAY 21,1906.

\NVEN'TOR BY v ATTORNEYS "UNITED sTATE- PATENT oFF1cE.-

GEORGE-T. peace, IOF'NEWARKJNEW JERSEY.

TWIST-DRILL. e

To all whom it may concern:

Be it known that I, Gnonon J. BnAco, a citizen of the United States, residing at Newark, in the county of lrlssexand State of New Jersey, have inventedv certain new and useful Improvements in Twist-Drills; and I do hereby declare the followingto he a full, clear, and exactdescription ot' tlie sarne, such as will enable others skilled inthc art to which it appertains to make and use the same.

My invention relates to improvements in drills and consists in improved-means for breaking up the chips, and in other features as hereinafter more particularly described and pointed out in the appended claims.

The object of my invention is to increase-the cutting speed and the eiliciency of drills.

i 1 will now proceed to describe my invention with reference to the accompanying drawings, illustrating one forth of drill embodying my invention and a cutter which maybe usedin forming the drill, and will then point out the novel features in claims.

In the said drawings, Figure 1 shows an elevation of the said drill; Fig. 2 shows a cross section thereof; Fig. 3. shows a cross-section of a milling cutter which may be used in forming said drill; Fig. 4 shows a side view of such cutter; and Fig. 5 is a view similar to Fig. 2 illustrating an alternative construction.

It is well known that the power required by metal cutting tools, and the spe'edof cutting, are greatly aliected by the character of the chip formed; and numerous attempts have been made to produce drills and other cutting tools capable of operating at higher speed and with less power than the drills commonly used.

I have found that drills as ordinarily constructed, cut too wide a chip, and that the cutting efficiency of the drill can be greatly increased by dividing the chip into a plurality of narrower chips. When this is done, by means such as hereinafter described, not only doesthe drill cut more easily, but it may be run at higher speed and does not heat up as fast as corresponding drills of the ordinary type. v

According to my invention I break up the cutting tat-e of each groove of the drill into aplurality of faces, which thereioreare relatively narrow as compared with the continuous cutting face of the ordinary twist drill, and which are separated b y what may be termed chip'- interrnptin'g faces, which preferably do not cut at; all, and in any case serve to break the continuity between the chip formed by one such sub-face and the chip formed by the next sub-lace. This I do, preferably,

and as shown in thedrawings, by forming the cutting face in a plurality of steps, the risers of which are Specification of Letters Patent. Application filed May 21,1906.' Serial N0.,317,'850.

Patented Oct. 8, 1907.

under-cut or reentrant so as to provide necessary clearancc.

7 Referring now to the drawings: and at first to Figs. 1 and 2 thereof, 1 designates a twist drill, which is like or dinary twist drills in that it is provided with,aplurality.

of spiral grooves 2 and with a conical point 3; but the drill differs from ordinary twist drills in that the said grooves, instead of having continuous-cutting faces as in ordinary drills, have their cutting faces broken up into a plurality of relatively narrow stepped faces 4, the risers 5 of which steps are undercut somewhat, as indicated, so that'these risers do not themselves form cutting edges.- Each of these steps 4 acts as an independ: ent cutting edge and forms an independent relatively 6 .narrow chip which is far more flexible than the wider chip of the ordinary drill and tends to break up more readily. The power required for the formation of these relatively narrow chips is apparently much less than that required for the formation ofasingle chip of breadth equal to the aggregate width of cut of the several steps of each cutting face.

' It is desirable that the edges of the corresponding chips formed by thetwo sides of the drill shall be staLg-' gored relatively: By so doing the work of the drill is 7.5 distributed moreunil'ortnly and better cutting assured. For this purpose therefore, I stagger the steps 4 on the two sides of the drill; for example, referring to Fig. 2, the innermost step l on the right hand side of said figure K is relatively narrow while the corresponding step on the left hand side of said drill is wider but not as wide as the combined width of the first two steps on the right hand side. The formation of the stepped cutting faces of the twist drill offers no, ditficulties if a cutting tool of proper form he used. In Figs. 3 and 4 I illustrate a milling cutter such as may be used, the same comprising teeth 6 having serrations 7 corresponding to the several steps on one cutting face of the drill. This milling cutter may be used in the ordinary manner.

bvionsly in order to stagger the steps of the two sides oi the drill, different but corresponding cutters must be used for the two sides.

It is not necessary that the sectional contour of the cutting faces 4 shall be straight, as shown in Fig. 2. To

the contrary, these faces may be somewhat concave, as

indicated in Fig. 5. I consider it important, however,. that the risers 5 of the steps shall be slightly under-cut or rentrant to an extent sufficient; so that the radius at the base of the riser shall not be greater than the radius at the point. If this were not the case, the edges of the risers would offer additional resistance; and if the risers,

' instead of being under-cut were outwardly curved, the

. effect would be to extend the length of the cutting edge, 2. A longitudinally grooved drill huvlng u plurality of v (ll. 2 A z 1 '2 whuch would then be substantlally one contmuous but longml m glooves md h qub M00: in gmd V mnln grooves extending to the cutting end of the (lrlll, 15 c v d g As above statedthe oblect 0[ y mven each of said sub-grooves being provided \rlth an overion' i's'toform a plurality of narrow-chips instead of a hangingedge, the sulrgroovgs of {he said main gl'bovos 5 single wide chip, and to this end I divide each cutti Staggered tive y so a th w mx mr cdL' of fiw of the drill into a plurality of continuous but p the sub-grooves of the dllferent mnln grooves do not track.- I In testnnony whereof I nfllx my slgnnture, In the pres- 20 embly pp facesence'of two \vll'nessos.

W at I claim is;

V -3?, A longitudinally grooved drill llnvlnp: sulrgrooves ln GEORGE "10 u'jgroove thereof extending to the cutting end of the drill, Witnesses:

ench 401T the said sub-grooves being provldedw wlth an H. M. MAnnLE,

A hanging edge. ROGER ll. LYON. 

